As a battery pack comprising a plurality of battery cells, such a one as discussed in Patent Document 1 has been known. In the battery pack mentioned in Japanese Patent Application Publication No. 2011-60623, a plurality of battery cells having positive and negative electrode terminals formed of different metals are stacked, and adjacent electrode terminals are connected with each other by clad material metal plates.
Additionally, there is also known a film sheathed battery to which a laminated film is used, as discussed in Japanese Patent Application Publication No. 2014-32924. The film sheathed battery described in Japanese Patent Application Publication No. 2014-32924 is configured in a manner to draw positive and negative terminals (named as tabs) outward.
In a structure where a plurality of film sheathed batteries of Japanese Patent Application Publication No. 2014-32924 are stacked such that the positive terminal and the negative terminal are alternately aligned, if the positive terminal and the negative terminal of adjacent film sheathed batteries are connected through a clad material, the structure is provided to have a three-layer structure interposing a plate-like clad material between the positive terminal and the negative terminal. Accordingly, when attempting to connect both of the two terminals to the clad material by applying a laser only from the side of either one of the terminals, there has arisen a problem that the intensity of the laser becomes weakened before the laser reaches a bonding surface formed between the other terminal and the clad material due to dispersion of the laser beam and the like.
The present invention was established based on the above-mentioned problem, and the object of which is to provide a battery pack tab welding method which can reliably bond tabs to the both surfaces of clad material.